A High Dynamic Range (HDR) technique is a known function for increasing display image quality. An HDR signal can have luminance information of about 10000 nits (cd/m2). Therefore, using an HDR technique enables an increase in luminance and contrast, which can enhance the impact of video. For example, Blu-ray (registered trademark) Disc adopts the HDR technique.
The luminance displayable by a display device has, however, an upper limit. Even when a signal (HDR signal) generated by the HDR technique is input, the luminance indicated by the HDR signal may be impossible to display.
PTL 1 and PTL 2 each describe a technique for adjusting the luminance of a display device. PTL 1 discloses a technique for adjusting luminance by calculating a typical gradation value of each dimming unit domain in accordance with input image data, generating, with reference to a target gamma curve, a target luminance value corresponding to the typical gradation value which is calculated, and calculating an emission luminance value in each issuance unit block in accordance with the target luminance value.
Moreover, PTL 2 discloses a technique for adjusting the luminance of an OSD image by determining an OSD signal to be output by using gradation data associated with the feature of a video signal to be displayed in a display area of the OSD image.